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Respiratory part of the lung
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Morphological Analysis
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The primary function of the respiratory system is gas
exchange
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The tissues cells
within the body lie too far from the air that is inhaled to allow the exchange of
gases in a direct manner
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This happens during each breath that is taken whereby
the oxygen first enters the mouth or nose via inhalation
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The trachea then splits into two
bronchi
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The bronchial tubes form many pathways within the lungs
and terminate at the end with a connection to a small sac called alveoli
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Exhalation begins after the exchange
of gas and the carbon dioxide containing air returns through the bronchial
pathway back to the external environment through the mouth or nose
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This is inclusive of the vocal cords in the
larynx for the production of sound, the lungs for homeostasis of the PH level
in the body and the olfactory bulbs in the nose for the sense of smell
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Functionally, there is a conducting zone, which is from the nose to
the bronchioles; this consists of the respiratory organs that are involved in
forming a path to conduct the inhaled air into the deeper lung region
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Anatomically, the respiratory system can be separated into
the lower and upper respiratory tract
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The upper respiratory
tract includes organs outside the cavity of the chest such as the nose pharynx
and larynx
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The cavities are narrow
canals that are separated from each other via a septum composed of cartilage
and bone
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The entrance for the nasal cavity located in the vestibule region is the surface
wall, which is made of squamous epithelium
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The main nasal passage is lined with
respiratory mucosa made of pseudo-stratified columnar epithelium containing
goblet cells
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The mucous traps dust and bacteria whilst
the antibacterial enzymes destroy particulates
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The conditioning and heating of inspired air happens through veins that are
present under the nasal epithelium
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During the course of breathing the nasal cavity geometry can be affected by
the nasal cycle
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This asymmetry is referred to as the
nasal cycle which is a result of congestion of the cavernous tissues of the
mucosa in one nasal cavity while at the same time decongestion (shrinking)

occurs to the erectile tissue in the other cavity
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The Pharynx
The pharynx is a funnel shaped passageway that is about 12
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It
connects the posterior nasal and oral cavities to the oesophagus and larynx
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It has three parts:
the nasopharynx which the where the nasal cavity opens above the soft
palate, the laryngopharynx and the oropharynx
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The
larynx lies at the top of the trachea
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The food or air is directed down correct passageway, either the trachea or the
oesophagus by being controlled by the epiglottis
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During swallowing, the soft palate and its uvula point upwards closing the
nasopharynx so that neither air nor food can pass through it
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The connection opens and closes to
equalise the air pressure in the middle ear to that of the atmosphere for the
conduction of sound
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This is the same epithelium found in the nasal
cavity and similarly the same mechanism of mucous secretion from goblet
cells in the epithelium to filter, warm, and humidify the inhaled air occurs here
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The Larynx
The larynx is a cartilaginous organ that acts as a passageway for air between
the pharynx and the trachea
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The airway
cavity of the Larynx extends at the epiglottis to the cricoid cartilage where it
can be found to be a continuous lumen of the trachea
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The vestibular folds are the upper folders and the true folds are vocal
folds
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The

interior surface of the superior portion of the larynx consists of stratified
squamous epithelium
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Below
the vocal folds the epithelium is pseudo stratified ciliated columnar
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Trachea
The trachea is a crucial part of the lower respiratory tract
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The wall is made up of
connective tissue and smooth muscle
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The mucous membrane that lines the trachea has an outer layer of pseudo
stratified ciliated columnar epithelium
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It’s called this
because the trachea splits into the left and right principle bronchus, which
then branches out into more progressive airways
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The diameter of the cross section in normal
adult males is 1
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5cm and is a little smaller in females
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There are 16-20 rings which stop the trachea
from collapsing on itself but it does also provide neck movement and
therefore, flexibility
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The tracheal mucosa has pseudo
stratified ciliated columnar epithelium whilst its submucosa has contains
cartilage, seromucous glands and smooth muscle
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The right bronchus is wider, shorter
and more vertical than the left
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The main right
bronchus splits inferiorly and posteriorly into the right upper lobe bronchus
and an intermediate one
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The left one goes inferolaterally at a greater angle from the axis that is
vertical in comparison to the right bronchus
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The main right bronchus has
three secondary bronchi and the left one has two
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Embryonic Aspects and development
The respiratory system doesn’t carry out gas exchange until after birth
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The lungs have four histological phases of development and in
the later fetal development respiratory motions, thyroid hormone and amniotic
fluid have a large role in the maturation of the lungs
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They are derived
from the same progenitor cell
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The development of this system doesn’t become completed until the last few
weeks of fetal development and therefore, premature babies have difficulties
associated with not having enough surfactant
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The lungs
as a organ for breathing must be developed to a certain extent that supports
the function of breathing immediately after birth
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During
intrauterine life the lungs are a very important source of amniotic fluid as
mentioned above
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The
lung maturation with the functional development and the lung growth which is
also knows as the structural development are the two phases
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The
maturation and the reaching of functionality is mainly a biochemical process
and its under the control of various hormones
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There is a progressive branching of the airway and finally the
development of the alveolar spaces allows gas exchange to happen in the
final trimester
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It prevents the alveolar from collapsing
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The surface
area by the end will be 50-100 m2
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The embryonic stage is the first stage and is present in the threeweek-old embryo
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The way the
lungs separate happens with the fusion of the easophagotrachseal ridges to
from the easophagotracheal septum
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The lung buds go on to form three
lobar buds which develop in the right lung bud and the 2 lobar buds in the left
lung
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The conducting airways are developed by
the branching
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Endodermal buds of the lung undergo branching only and if they are exposed
to the bronchial mesoderm
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All bronchial airways
are completed by the 16th week
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At this point the differentiation of the epithelium of the
lungs happen
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For the
epithelial differentiation of happen, mesenchyme is needed and there is a
transition from the formation of the bronchial epithelial cells to the alveolar

type 2 cells
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The third stage is the canalicular stage is present in the 16th-25th week
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There is a significant decrease of the interstitial tissue and the growth of the
capillary network
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The type 1 pneumocyte is the main structural cell of the alveolus, and the
exchange of gas will occur across the membrane like cells
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At
around the same lamellar bodies will be seen and inclusion bodies in the
second type of alveolar cells
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The next stage is the saccular stage, which can be named the terminal sac
occurs from week 26 until term
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As this stage goes on there are type 1 and
2 type cells
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Lung stability is proportional with the number of lamellar bodies
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At birth the air containing space becomes the
alveolus and is called the primitive saccule
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The shape of the saccule doesn’t achieve
adult form until 5 weeks after birth
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It’s lined with type 1 cells, which contact the pulmonary
capillaries
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The
blood/air interface has type 1 cells, a basements membrane and the
pulmonary capillary endothelium
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Development of

and the branching of the pulmonary artery mirrors the bronchial branching and
later it mirrors alveolar development
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The alveoli are composed of a single layer of
squamous epithelium
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The respiratory bronchioles have single alveoli off their walls
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The respiratory
bronchioles lead to the alveolar ducts, which lead to the sacs
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About 100 million alveoli are found in each lung
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2mm in diameter
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The alveolar sacs are spaces surrounded by clusters of alveoli
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Alveolar sacs usually occur at the end of an alveolar duct but can occur
anywhere along the length
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Gas exchange between blood and air occurs across a highly specialized
region of the pulmonary alveolus, the blood-air barrier, or alveolar-capillary
membrane which is readily permeable to gases via diffusion
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A thin layer

of surfactant produced by type II pneumocytes also covers the alveolar
surface
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Adjacent pneumocytes
are sealed by tight junctions, which prevent leakage of fluid and solutes
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Ultra structurally, endothelial cells are arranged as an interlocking,
contiguous mosaic
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Immunocytochemistry has shown that microvilli react
to antibodies to angiotensin-converting enzyme, whose inhibitors are used to
treat congestive heart failure
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Organelles are almost entirely
absent in slender extensions of endothelial cells, which in some areas may be
quite thin—only 0
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The most striking feature of these cells is the
presence of numerous vesicles, which are free in the cytoplasm or closely
associated with luminal and abluminal cell surfaces and whose main function
is to transport fluid and proteins between blood and surrounding interstitium
Type II pneumocytes are cuboidal cells that measure 10–12 µm in diameter
and possess a distinctive ultrastructural appearance
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Short stubby microvilliproject from the cellular surface
into the alveolar lumen
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Large, pleomorphic membranebound multilamellar bodies , a unique feature of these cells, can be observed
extruding their contents into alveolar spaces
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They are
derived from the Golgi complex and are ultimately discharged by exocytosisat
the cell surface
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Surfactant's detergentlike property prevents collapse of alveoli by reducing surface tension, thereby
facilitating alveolar inflation during inspiration
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This replicative potential is important for healing after lung
injury, because the large surface area of type I cells makes them especially
susceptible to damage
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They are usually seen bulging into the alveolar space, often situated at
junctions between adjacent interalveolar septa
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Their cytoplasmcontains various
organelles, including many primary and secondary lysosomes
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Their main function is to ingest dust and other
foreign particles that have entered alveolar spaces during inspiration
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These motile cells are derived

from blood monocytes whose precursors arise in bone marrow
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They
undergo maturational division in the interstitium of the lung and then enter
alveolar spaces to lie free in the lumina
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In certain types of heart
disease, such ascongestive heart failure, erythrocytes from the bloodstream
may escape into pulmonary alveolar spaces, where alveolar macrophages
may phagocytose them
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Clinical Aspects
There are several well-known examples of failure of normal physical
development of the lung
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The syndrome has an
incidence of approximately 1:3000 births
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Ninety percent have blind upper esophageal pouch
and connection of distal esophagus to lower trachea
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This
occurs predominantly on the left side
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Finally, we cannot ignore the supremacy of the lung compared with
other organs
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It is caused by defective transport of chloride ions in mucous cells of
seromucous glands in the respiratory tract as well as in cells producing sweat
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CF transmembrane conductance regulator is a
channel that control the movement of chloride in and out of the cell
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Respiratory failure is the most
serious consequence as it can be life threatening
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Often paired with the common cold or allergies
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The condition causes
excessive buildup of mucous causing the drainage pathways to become
obstructed and function improperly
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Kartagener syndrome is a rare genetic disorder, which is characterised by
situs inversus, sinustisis and chronic enlargement of the bronchial airway
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It’s
aetiology Is unknown
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It
can become apparent in neonatal life which chronic upper and lower
respiratory tract disease resulting in defective mucocillary clearance
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There is acute bronchitis, which has a shorter duration and follows viral
infections
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Chronic
bronchitis is long lasting and is recurrent
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Symptoms include persistent cough as well as increased sputum production,
plugging the lower airways
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Symptoms include dyspnea, coughing,
wheezing, etc
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The primary function of the respiratory system is
gas exchange
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References:

http://discovery
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com/in-vivo-development/lung
https://www
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com/physiology/textbooks/boundless-anatomy-andphysiology-textbook/the-respiratory-system-22/respiratory-system-diseasesdisorders-injury-and-clinical-cases-215/
http://www
...
nlm
...
gov/pubmed/15760593
https://www
...
com/en/library/anatomy/hilum-of-the-lung
http://teachmeanatomy
...
embryology
...
html
http://discovery
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com/in-vivo-development/lung



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